High-frequency heating generator



June 19, 1956 L. BLOK HIGH-FREQUENCY HEATING GENERATOR Filed Aug. 7, 1952 a. once a x .a.

g INV E NTOR LOUREN s BLOK United States Patent 50 HIGH-FREQUENCY HEATING GENERATOR Lourens Blok, Eindhoven, Netherlands, assignor to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application August 7, 1952, Serial No. 303,195

Claims priority, application Netherlands September 26, 1951 3 Claims. (Cl. 250-36) This invention relates to high-frequency heating generators comprising an electronic tube oscillator having a water-cooled primary or tank coil which is closely surrounded by a secondary or coupling coil in the form of a circularly bent metal. strip. The water cooling of the tank coil is required to enable the heat produced by the high-frequency losses in the coil to be conducted away. Generally the secondary coil has only one turn and is connected to the (external) heating coil, in the field of which the material to be heated is arranged.

In order to provide sufficient energy in the heating coil, the coupling between the primary and secondary coils should be comparatively tight and hence the secondary is required to surround the tank coil, for example, with a 10 w. generator the intermediate spacing is about 7 mm.

Under certain conditions this may give rise to arcing between the primary coilacross which potentials of many thousand volts may occur-and the secondary coil. This is found most likely to occur if vapour condenses on the oscillating coil and this may readily occur when the anode supply voltage of the generator is cut oit the other supply voltages remain connected (so-called stand-by adjustment). In this case, cooling water continues to flow through the primary coil (that is through the tubing of which the primary coil is wound) and cools it intensely, since heating by high-frequency current losses no longer occurs. The water may be cold enough for vapour from the atmosphere to condense on the coil and the drops suspended from the coil are readily liable to bring about a flashover to the secondary coil when anode voltage is again supplied.

According to the invention, a high-frequency heating generator comprising a discharge tube oscillator having a water-cooled tank coil which is closely surrounded by a secondary coil in the form of a circularly bent metal strip, is characterized in that the supply pipe for cooling water for cooling the coil contains an electrically controllable valve and control means are provided to permit flow of cooling water only when the generator is in use, but does not act to any appreciable extent on the supply of the cooling water to the anode of the oscillating tube.

In practice this may be realised by including the valvecontrol electro-magnet in a circuit in which the magnet winding is connected into circuit simultaneously with the anode supply transformer of the generator. In this case, cooling water flows only when the anode supply voltage of the oscillating tube is connected into circuit and does not flow when this voltage is cut oil, the coil being thus prevented from becoming cooled to a temperature lower than the temperature of the atmosphere.

The invention will now be described with reference to the accompanying diagrammatic drawing, given by way of example, in which:

Fig. l is a perspective view of the essential parts of an embodiment of the invention, and

Fig. 2 is a sectional detail view thereof.

Fig. 1 shows a water-cooled coil system of a highfrequency heating generator comprising a primary coil 1 Wound from copper tubing and a copper strip 3 which, bent to form a cylindrical shell closed but for a small slit, is arranged to surround the coil co-axially and constitutes a secondary coil. Along the edges of the small slit the copper strip is bent outwardly at right angles thereto and the two ends 3 and 3" of the strip are arranged spatially parallel to one another with a very small intermediate space of, say, one millimeter, are substan tially radial to the circularly bent part and constitute connections to a heating coil (not shown) which may be screwed to two copper connecting blocks 5 and 7 secured to the ends 3 and 3", respectively.

The coil 1 is wound on a support comprising three radially arranged strips 9 of low-loss insulating material which each has one end secured to a vertical metal wall which forms part of a transportable frame 11. The coil 1 can be moved into and out of the secondary coil 3 to vary the coupling and thus control the output energy.

T he coil 1 has cooling water fed to it through a flexible tube 13. The cooling water passes through the coil 1, a second rubber tube 15, a connecting pipe 17, flexible tubes 19, 21 and 23, and hence flows through the con necting blocks 5 and 7, and passes finally through a discharge pipe 25.

Other parts of the cooling system and the discharge tube are arranged behind a screening plate 27.

The maximum coupling between the coils 1 and 3 is required to be very tight in order that in practice it may be possible at any load to feed the maximum energy to the heating coil. The diiierence in spacing between the primary and secondary coils is therefore small. With a 10 kw. generator, the spacing is about 1 cm., the primary coil having a diameter of about 30 cm. Due to divergence from exact co-axial arrangement of the coils 1 and 3 which can only with difiiculty be avoided, a minimum spacing of about 7 mm. may be assumed. This is sufficient to avoid arcing between the coils under normal conditions.

When in use, the operation of the generator is continuously interrupted temporarily by switching off the anode supply voltage of the thermionic tube, the other supply potentials and auxiliary potentials remaining connected. If cooling water were permitted to continue to flow when no heating of the core 1 by high-frequency losses in the coil 1 was taking place, the coil might be cooled by the cooling waterthe temperature of which may be 12 C.-to below the dew point of the surrounding atmosphere with the result that vapour would condense on the coil and drops suspended from the coil 1 would be liable to bring about arcing between the coils l and 3 on the anode voltage again being supplied to the discharge tube. In order to avoid this disadvantage, the water supply pipe contains an electrically controllable valve 29 which permits flow of cooling water only when the generator is in use but does not act to any appreciable extent on the cooling circuit for the anodes of the oscillating tubes. The valve shown in Fig. 2 is of known construction and comprises a stud 31 having a conical end which in its normal position closes an entry-port 33, thus shutting oil? the flow of cooling water. The valve control device comprises an electro-magnet 35 the armature 37 of which, on energization of the magnet, raises the stud 31 against the pressure of a spring 39.

This takes place when the anode supply transformer 41 is connected into circuit. For this purpose, the magnet 35 may be included in an auxiliary circuit which is established and broken by a contact of a relay 43 by which anode-voltage supply transformer 41 is controlled. The flow of cooling water through the coil 1 is consequently interrupted when the generator is not in use; the water that may be available within the coil is always warm enough to avoid condensation.

The device described above is not efiective if the oscillator stops oscillating for a short period due to a fault or to excessive load and thereafter again starts to oscillate, in which case condensation of vapour on the coil and arcing are therefore liable to occur. If desired, this may also be taken into account, for example, by energizing the magnet 35 with the use of a direct current obtained by rectification of a small part of the high-frequency output current of the tube or with the use of a current controlled by such rectified current With the aid of a relay or relays.

What I claim is:

1. A high-frequency generator comprising; a discharge tube oscillator provided with a water-cooled anode, a water-cooled primary coil operatively connected to said oscillatory, a secondary coil in the form of a circularly bent metal strip surrounding said primary coil with relatively small spacing therebetween, a water supply pipe for cooling the primary coil, and an electrically controllable valve in said water supply pipe including an armature, a source of electrical current, an electromagnet which upon magnetization operates said valve to permit the flow of cooling water only when said generator and said electromagnet have said current applied thereto but does not interrupt the continual supply of water to the anode of said oscillator.

2. A high-frequency generator as set forth in claim 1 wherein said electrically controllable valve is provided with a circuit having an anode supply transformer for said discharge tube oscillator and said electro-magnet therein, and means connecting the electro-magnet into said circuit simultaneously with said anode supply transformer.

3. A high-frequency generator comprising; a discharge tube oscillator provided with a Water-cooled anode, a water-cooled primary coil operatively connected to said oscillator, a secondary coil in the form of a circularly bent metal strip surrounding said primary coil with relatively small spacing therebetween, said circularly bent metal strip having two elongated ends extending radially from said metal strip and transverse to the axis thereof, said two ends being parallel-spaced and each having a connecting block secured thereto, a water supply pipe for cooling the primary coil, and an electrically controllable valve in said water supply pipe including an armature, a source of electrical current, and electromagnet which upon magnetization operates said valve to permit the flow of cooling water only when said generator and said electromagnet have said current applied thereto but does not interrupt the continual supply of water to the anode of said oscillator.

References Cited in the file of this patent UNITED STATES PATENTS 1,987,458 Adams Jan. 8, 1935 2,138,181 Lindenblad Nov. 29, 1938 2,403,969 Fledel-Beck July 16, 1946 2,404,404 Robends July 23, 1946 2,455,822 Storm Dec. 7, 1948 2,672,544 Finchelstein et al. Mar. 16, 1954 

